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jpx(at)Qenesis.com
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 Posted: Thu Nov 13, 2008 9:11 pm Post subject: Static in radio reception |
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A friend of mine is flying a Citabria. It is quite new, but suffered
in a crash. I was completely rebuilt/restored and is now again a
beautiful airplane.
It has one snag. Perhaps folks on the list have some ideas. The
symptom is that sometimes radio reception is unreadable. Scratchy
static overwhelms the voice audio. It is most obvious when within 5
miles of the control tower, since it is necessary to ask the
controller to repeat multiple times. Other times, aircraft from over
100 miles away are heard on common frequencies, or the controller is
clear, so sometimes the receive works very well.
Transmit is believed okay. The tower never complains about
transmissions, but this has never really been checked over greater
distances than 10 miles.
The radio is a new Garmin, which was swapped for a few days with an
identical model, which exhibited the same symptoms.
Consultation with the factory has yielded little. Mechanics have
checked phyical connections and continuity, and cut the fabric under
the antenna so the ground doesn't rely entirely on the screws. He has
tried different headsets.
The ground plane is a piece of aluminum about 6" wide and 15" long on
the back of the aircraft where the ELT antenna is typically installed.
There are about 8 wires, tied together and attached to the ground
plane about 4" ahead of the antenna, and these wires wrap down around
the fuselage to extend the ground plane. The ground plane is also
electrically connected to the steel fuselage tubing. This is all per
factory instructions. There are no adjacent antennas, and this
antenna is at least 4 feet ahead of the tail.
Reportedly, a VSWR test at the antenna gave a poor result, but I was
not involved in the test and I am not sure about the reliability of
the equipment or the person doing the test. The antenna is a new
Comant, with COM and GPS.
Most of the things I can think of being wrong would likely affect
transmit more than receive and not produce static.
I am currently thinking that perhaps the radio, antenna etc. are
actually fine, but are intermittently being interfered with.
I have suggested to the owner that when the problem occurs, he try
powering off the new PS Eng audio/intercom, which then gives him a
direct connection to the radio. I also suggested he power off the
transponder. If that fails to help, I have loaned him a new antenna
(I will be a while building yet) to try.
If that doesn't help ... ???
Does anyone have any other ideas that should be looked into ?
Thanks !
Jeff Page
Dream Aircraft Tundra #10
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jpx(at)Qenesis.com
Guest
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| Posted: Tue Nov 18, 2008 6:49 am Post subject: Static in radio reception |
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Does no one have any comments to offer on this ?
Thanks, Jeff
---------------------------------------------------------------------
A friend of mine is flying a Citabria. It is quite new, but suffered
in a crash. I was completely rebuilt/restored and is now again a
beautiful airplane.
It has one snag. Perhaps folks on the list have some ideas. The
symptom is that sometimes radio reception is unreadable. Scratchy
static overwhelms the voice audio. It is most obvious when within 5
miles of the control tower, since it is necessary to ask the
controller to repeat multiple times. Other times, aircraft from over
100 miles away are heard on common frequencies, or the controller is
clear, so sometimes the receive works very well.
Transmit is believed okay. The tower never complains about
transmissions, but this has never really been checked over greater
distances than 10 miles.
The radio is a new Garmin, which was swapped for a few days with an
identical model, which exhibited the same symptoms.
Consultation with the factory has yielded little. Mechanics have
checked phyical connections and continuity, and cut the fabric under
the antenna so the ground doesn't rely entirely on the screws. He has
tried different headsets.
The ground plane is a piece of aluminum about 6" wide and 15" long on
the back of the aircraft where the ELT antenna is typically installed.
There are about 8 wires, tied together and attached to the ground
plane about 4" ahead of the antenna, and these wires wrap down around
the fuselage to extend the ground plane. The ground plane is also
electrically connected to the steel fuselage tubing. This is all per
factory instructions. There are no adjacent antennas, and this
antenna is at least 4 feet ahead of the tail.
Reportedly, a VSWR test at the antenna gave a poor result, but I was
not involved in the test and I am not sure about the reliability of
the equipment or the person doing the test. The antenna is a new
Comant, with COM and GPS.
Most of the things I can think of being wrong would likely affect
transmit more than receive and not produce static.
I am currently thinking that perhaps the radio, antenna etc. are
actually fine, but are intermittently being interfered with.
I have suggested to the owner that when the problem occurs, he try
powering off the new PS Eng audio/intercom, which then gives him a
direct connection to the radio. I also suggested he power off the
transponder. If that fails to help, I have loaned him a new antenna
(I will be a while building yet) to try.
If that doesn't help ... ???
Does anyone have any other ideas that should be looked into ?
Thanks !
Jeff Page
Dream Aircraft Tundra #10
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gyoung
Joined: 09 Jan 2006
Posts: 211
Location: Republic of Texas
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| Posted: Tue Nov 18, 2008 8:56 am Post subject: Static in radio reception |
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You did not mention the cable. Replace it or do a temp trial with a known,
good cable. I too had that problem in a Citabria and a replacement cable
cured it.
Regards,
Greg Young
[quote] --
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Neal.George(at)hurlburt.a
Guest
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| Posted: Tue Nov 18, 2008 8:56 am Post subject: Static in radio reception |
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Jeff -
If the problem persists when you swap radios, then it's in the system.
Check the wiring again. I've experiences similar problems when the plugs at the back of the tray don't fully engage as the radio is seated.
Scratchy audio could result from dirty pins/sockets, mismatched pins/sockets, bad crimps, broken wires in intermitent contact, etc. It could also reside in the audio panel / intercom.
If the antenna is the correct length, the bad VSWR could result from impropper mating at the connector, bad crimps, dirty connectors, poor ground, etc.
neal
=================
Does no one have any comments to offer on this ?
Thanks, Jeff
---------------------------------------------------------------------
It has one snag. Perhaps folks on the list have some ideas. The
symptom is that sometimes radio reception is unreadable. Scratchy
static overwhelms the voice audio. It is most obvious when within 5
miles of the control tower, since it is necessary to ask the
controller to repeat multiple times. Other times, aircraft from over
100 miles away are heard on common frequencies, or the controller is
clear, so sometimes the receive works very well.
Reportedly, a VSWR test at the antenna gave a poor result, but I was
not involved in the test and I am not sure about the reliability of
the equipment or the person doing the test. The antenna is a new
Comant, with COM and GPS.
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psamuelian(at)charter.net
Guest
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| Posted: Tue Nov 18, 2008 12:58 pm Post subject: Static in radio reception |
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I agree with Greg. Start by replacing the antenna coax with a known
good cable. It may have been damaged in the crash and have an
intermittent center conductor. When transmitting there is enough
power to punch through to the tower even with the VSWR mismatch, but
reception is extremely low power and subject to signal degradation.
Just a guess...
Phil
RV7 Saving for wing/Cessna 177
On Nov 18, 2008, at 8:55 AM, Greg Young wrote:
[quote]
sol.com>
You did not mention the cable. Replace it or do a temp trial with a
known,
good cable. I too had that problem in a Citabria and a replacement
cable
cured it.
Regards,
Greg Young
> --
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